Field of the Invention
The present invention relates to an image pickup device and a method for manufacturing the same.
Description of the Background Art
Image pickup devices are generally classified into a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS) image sensor. In recent years, CMOS image sensors are produced using copper (Cu) as a material for an interconnect. In order to prevent the copper from diffusing from the copper interconnect, a liner film (SiN, SiCN, etc.) is deposited on the copper interconnect as an anti-diffusion film. A technique using such a liner film is described for example in Japanese Patent Laying-Open No. 2009-302565 etc.
A process for processing a semiconductor device includes a heat treatment referred to as a sintering process, in which for example a dangling bond generated in a gate oxide film is terminated by hydrogen. When a liner film is deposited, as described in Japanese Patent Laying-Open No. 2009-302565, the liner film does not let hydrogen pass therethrough easily, and the dangling bond cannot be terminated sufficiently. This prevents an interface state density from recovering, and at a dark period, in particular, a dark current flows, resulting in degraded dark characteristics. The degradation of the dark characteristics is significant at the four corners of a pixel sensor area as seen in a plan view, in particular.
In order to improve the above dark characteristics, the liner film has a region removed by techniques described for example in Japanese Patent Laying-Open Nos. 2010-278232, 2012-104654, etc.
Japanese Patent Laying-Open No. 2010-278232 describes removing a liner film other than that on a copper interconnect of a pixel region and that of a circuit formation region. The publication describes that this allows the pixel region and any other region to have hydrogen introduced into a substrate in uniform amounts, respectively, and thus have their semiconductor devices with their characteristics matched.
Furthermore, Japanese Patent Laying-Open No. 2012-104654 describes providing a dummy pixel region with a dummy via interconnect penetrating a liner film. The publication describes that the dummy via allows hydrogen to diffuse therethrough to thus suppress a difference otherwise caused between a pixel region and the dummy pixel region in their dark characteristics.